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So, by the very fact that this thread's content contains more information than a single semester of junior college... Proves that Subarus, albeit quirky are a thinking mans car! *Yes, there are boy-racers/ricers about that own many Scoobies, but as a whole, I've rarely witnessed a more multi-syllabic dialog!

[And we now return you to your regularly scheduled injector cleaner conversation...]

It can be purchased at your local Napa or online. Add it right before you top off your tank and run it down. "That stuff will suck the paint right off your house and give your family a permanent orange afro!" - Dan Akroyd

When all you have is an 'indirect' means of measuring as you call it, that is what you are stuck using. Measuring O2 in the exhaust stream to correlate AFR is not indirect. Inaccurate to a degree, yes. At the time, it's all the engineers had to work with. Unless they're wrong too.... Hence the development of wide band O2.

The problem is that the O2 sensor does one thing: It measures oxygen content relative to an external sample. It has no idea if proper combustion has taken place, or, indeed, if any combustion has taken
place. To it, there is no difference between an exhaust composed solely of atmospheric gasses during fuel-cut overrun and exhaust lousy with unburned fuel due to a misfire. There could be a river of unburned fuel flowing down the exhaust pipe, and as long as the zirconium sensor doesn't get contaminated, it could still see a "lean" environment.

A device that can not tell you if combustion took place does not tell you anything about combustion.
We only infer, and tell ourselves that we "know". We assume that the norm is proper ignition, reasonable combustion, and the composition of the exhaust gasses will be within a narrow range. And boundaries are generally not considered, although out-of-bounds, beyond-limit situations occur all around us.

In order for the O2 to read anything other than base line O2 (.495 volts) it has to be heated to a high temp and then it starts creating a voltage based on the O2 in the exhaust stream. You sure ain't heating it with a hairdryer.... And now I know why GD gets the way he does in discussions like this. No offense intended Rick. lol

The guys in the shop and our area state emissions rep are really getting a good laugh out of this post, so I'm just going to let it ride.....

I understand; I have annoyed Rick and others at various times. Regardless of what is correct, incorrect, perspective, or whatever, it is hard to properly convey a point of view in a series of posts. I truly was not trying to criticize, nor change your view; especially since it is the popular and accepted view. Sometimes, though, it helps to try looking at things from a different perspective.

If I have brought a little laughter into your life, then I am OK with that.

not to stir old, but i agree with skishop. ghe just explained it better than i felt the need to. 90% of the cars on the road will see little to no benefit from injector cleaning solutions, unless they have actual physical dirt/grit that has made it past the fuel filter. the reason that solution was ever used in the first place is because it really works on carburetors. carburetors are a passive fuel system, where it is drawn via vacuum mostly, aside from accelerator pump circuits. in a fuel injection system, its pressurized anywhere from 20-60psi, simply the fact that its under pressure means systems can go decades without need for cleaning, as long as the fuel filter does not give way. the pressure blasts most soluble things right through without a hiccup. anything solid has the potential to clog and cause continuous leakage. the only way it will ever improve mileage is if the injector can no longer regulate fuel flow to what it was intended to deliver.

for example, say the fuel system is designed to flow 50lph. yours has a clogged filter, which cuts fuel flow in half. your car suffers from power loss, but is otherwise still driveable with a system that only flows 25 lph. even if the o2 reads lean, it can only enrich so much, especially with half of the intended fuel flow. in fact, no matter how much it enriches, it can only use 25lph. this case is just figurative, and the numbers pulled outta my butt, but the principle is the same. this lean condition wont help you pass emissions, but it does answer the question if cleaning will help mileage.

as far is spray pattern is concerned, its not really a concern with our motors, or really TBI cars for that matter, because the TBI system was based off starting the fuel by the throttle plate, like a carburetor, so that engine vacuum and a heated intake can assist in the full atomization of fuel. as far away as it is from the combustion process, the spray pattern could be and the driver wouldnt know unless he/she was extremely vigilant and noticed a single hp missing.

also, i might be new here, but im no stranger to cars. ive been responsible for a few spec miata motorsports race team successes, associates degrees in auto tech and hi-po engine building and tuning, working on a mechanical engineering degree. my own ea82 has a straight pipe, catless exhaust, and still passes emissions without any sneaky tricks thanks to a wideband o2 sensor and ported heads. im not new to this, thats for sure.

I could have been more clear in stating the Lambda (or wideband) O2 sensor measures actual AFR. As for intake design information, if you're really that interested, the info is out there. Other than that, I apparently need to tell all my instructors and my friend with a Masters in internal engine combustion design who works for Rausch racing that they have been giving me bad information.

That first article on O2 sensors was good reading. I noticed this part:

Unheated 1 or 2 wire wire O2 sensors on 1976 through early 1990s vehicles can be replaced every 30,000 to 50,000 miles.

I replaced my original non-heater sensor at 130K only after it threw an engine code so I think I got my money's worth out of it.

Just got back from a 110 mile trip. I got 34 MPG so I think there isn't any worries as far as fuel economy go especially considering the original highway ratings for my 93 Loyale were 29 on the highway.